Vehicle manufacturers are increasingly including antilock braking systems (ABS) on vehicles. These systems are designed to increase the ability of a vehicle operator to bring a vehicle to a stop on road surfaces, even if the surfaces are slippery.
In an ABS system, it is desirable to perform a cycle test of certain ABS system components to determine their functionality prior to a time the vehicle operator requires the system to perform antilock functions. Typically, this cycle test is performed once the vehicle ignition is turned on, or shortly thereafter once the vehicle attains a predetermined speed. Although some ABS systems rely on master cylinder pressure, other systems include a motor which drives a pump for creating system pressure. In these latter systems, it is desirable to test the functionality of the motor, as well as other system components, such as solenoid valve coils.
Referring now to FIG. 1, there is shown an existing methodology for testing the motor of an ABS system. As shown, the motor is energized with a single step input electrical signal V(t) having a duration of approximately 0.5 S after which the excitation is removed. If the motor is not functional (e.g. rotor locked), the signal V(t) will substantially instantaneously return to zero at t.sub.2 as shown in FIG. 1. If, however, the motor is operational, application of V(t) across the motor will result in rotation of the motor rotor. As a result, the motor generates what is known as a back-emf after removal of the excitation voltage, and the signal will decay to zero, as shown by the dotted line. As a result, prior art methodologies look for the existence of this back-emf as an indication of the functionality of the motor.
When the motor is energized with V(t) and the pump is driven, there is an accompanying audible noise emitted which may be heard by the vehicle operator. The perception of this noise by the vehicle operator is undesirable.
As such, there is a need for an ignition cycle test that satisfactorily tests the appropriate ABS components, such as the pump motor, while minimizing motor rotational speed and motor operating time so as to minimize perception by the vehicle operator of the noise accompanying motor operation.